The present invention relates to gripper blocks installed in coiled tubing injection equipment used in the oil and gas production industry. More specifically, the present invention relates to a gripper block designed to better accommodate lengths of coiled tubing with varying outside diameters.
Reeled or coiled tubing has been used for many years for performing certain downhole operations, including but not limited to completions, washing, circulating, production, production enhancement, cementing, inspecting, and logging. There are a number of patents issued on coiled tubing injectors and related equipment. Such injectors generally use a pair of opposed endless gripper chains mounted in a common plane. The gripper chains are normally made up of links, rollers, and gripper blocks. Opposed gripper blocks on the endless chains engage the tubing as to firmly grasp the tubing in such a way that the gripper blocks will force the tubing into or out of a wellbore when the gripper chains are driven. Upon setting the gripper chains into motion and upon each opposing pair of gripper blocks releasing their hold on the tubing, another pair of opposed gripper blocks grippingly engage the tubing and the cycle continues until a desired amount of tubing has been inserted into or withdrawn from the wellbore, or until the gripper chains are no longer driven.
Over the years, a variety of gripper blocks have been developed to improve the performance of coiled tubing injector units. Such improvements include designs directed to increasing the load carrying capability of gripper blocks, thus eliminating or limiting scarring and distortion of the tubing caused by gripper block engagement; providing the ability to accommodate differing tubing diameters without having to change gripper blocks; reducing the weight of gripper blocks; and reducing the manufacturing costs of gripper blocks. Such prior art gripper blocks are disclosed in U.S. Pat. No. 5,094,340 to Avakov, issued Mar. 10, 1992; U.S. Pat. No. 5,853,118 to Avakov, issued Dec. 29, 1998; and U.S. Pat. No. 6,230,955 B1 to Parks, issued May 15, 2001; each of these patents being assigned to the assignee of the present invention and the details of each of these patents being incorporated herein in its entirety by reference.
In the past, coiled tubing has had a constant cross section. However, maintaining a constant diameter for the tubing can present some problems under certain circumstances. For example, it may be desirable to reduce the weight of the string or to reduce the amount of drag in the wellbore by reducing the diameter of the tubing. Additionally, small diameter tubing is preferable if the size at the treatment area is particularly small or confined. However, it is also noted that smaller diameter tubing tends to buckle more readily than large diameter tubing and that smaller diameter tubing also presents significant pressure drop problems in longer tubing strings. It is notable that each of these problems with both large and small constant diameter tubing may beaddressed by allowing the use of larger outside diameter tubing at the top of the string and a smaller outside diameter tubing at the bottom of the string proximate to the treatment zone. One convenient way of linking or connecting coiled tubing having varying outside diameters utilizes one or more tapered connectors in the tubing string. Such a tapered connector generally comprises at least a first tubular portion having a first tubing outside diameter, a second tubular portion having a second tubing outside diameter which is different than the first, and a tapered portion disposed between the first and second tubing portions. One such tapered connector for a tubing string is disclosed in U.S. Pat. No. 6,367,557 B1 to Rosine et al., issued Apr. 9, 2002; this patent being assigned to the assignee of the present invention and the details of this patent being incorporated herein in its entirety by reference.
The tapered connector, according to Rosine et al., and the improved gripper block designs, according to Avakov and Parks, make it possible to insert coiled tubing into a well using a twin carriage coiled tubing injector apparatus as known in the art. One example of a twin carriage tubing injector apparatus is shown in U.S. Pat. No. 5,553,668 to Council et al., issued Sep. 10, 1996; this patent being assigned to the assignee of the present invention and the details of this patent being incorporated herein in its entirety by reference. Although it is possible to stop the injector apparatus to adjust the spacing between the moveable gripper chains to accommodate varying outer tube diameters, it would be desirable to have an improved gripper block to accommodate abrupt changes in the outer diameter of jointed tubulars and tapered strings without costly stoppages to make adjustments or modifications. Accordingly, there is a need for an improved gripper block capable of not only engaging the surfaces of tubing having changing outer diameters but to conform rapidly to these changing geometries and reduce the number of stoppages for adjustment or modification required in standard twin carriage tubing injector apparatus.